There are several API types of ring gaskets used in BOP connections and this is very important to personnel involving in drilling operation to know about it. API 6A: Specification for Wellhead and Christmas Tree Equipment is the standard which every manufacture refers to their equipment.
API Type R Ring Gasket
The API type “R” rig gasket is not a pressure energized gasket therefore this type does NOT recommend for BOP equipment or safety critical equipment as x-mas tree, wellhead valves, etc. Sealing area is along small bands of contact between the gasket and the ring gasket on both ID and OD of the gasket. Shape of type “R” may be oval or octagonal in cross section (see Figure 1). Additionally, face to face between flanges will not touch when the flanges are tightened (see Figure 2). The “R” gasket is compatible for 6B flanges.
Figure 1 – Type R ring gaskets (shape and groove)
Figure 2 – Type “R” Gasket When Energized
API Type “RX” Ring Gasket
RX ring gasket is a pressure energized ring joint gasket and sealing area when energized is along small bands of contact between the groove and the OD of the ring gasket (see Figure 3). This gasket is manufactured a little bit bigger in diameter than the ring groove therefore when it is compressed, it will deform and seal the pressure. The “RX” is also not a face to face contact (see Figure 4). This gasket must be utilized only one time. The “RX” gasket is compatible for 6BX flanges and 16B hubs.
Figure 3 – Type RX Ring Gasket (Shape and Groove)
Figure 4 – Type “RX” Gasket When Energized
API Face-to-Face Type “RX” Ring Gasket
The face-to-face “RX” ring gasket is similar to “RX” gasket except it has increased groove width to ensure face to face contact between flanges or hubs (see Figure 5). However, this leaves the gasket unsupported on its ID. It is pressure-energized gasket which was adopted by API. This gasket may not remain in a perfect round shape when it is tightened because it does not have the support from ID of the ring groove.
Figure 5 – Face-to-Face Type “RX” Ring Gasket
API Type “BX” Ring Gasket
API Type “BX” (Figure 6) is a pressure energized ring and it is designed for face-to-face contact between hubs or flanges. When energized, small contact bands between OD of the ring gasket and the rig groove is the sealing area. This ring gasket is slightly bigger than the ring groove. Therefore, when the hubs or flanges are tightened, the gasket will be slightly compressed into the rig groove to seal pressure (see Figure 7). Since this is face-to-face contact type, the tolerance of the gasket and ring groove is vital. If you have the gasket at the high side of tolerance and the groove at the low side of tolerance, it will be quite difficult to achieve face-to-face contact. The “BX” gasket is compatible for 6BX flanges and 16BX hubs.
Figure 6 – API Type “BX” Ring Gasket
Figure 7 – API Type “BX” Ring Gasket When Energized
Reference book: Well Control Books